1. Field of the Invention
The present invention relates to an apparatus and method for controlling communications on a network.
2. Description of the Related Art
With the recent improvements in electronics technology there is a tendency to install multiple devices in one piece of equipment, and the units for controlling this equipment over a network are becoming progressively larger. In a general communication network, there is also a tendency that the network is becoming complicated due to the spread of multimedia, etc.
When a network has a tree-structure with three or more layers, and when a communication method is adopted in which protocol data units (PDUs) (a general nomenclature of packets for carrying messages and commands) are transmitted from a lower order point (corresponding to a node on a network) to a higher point, and the PDUs are collected at the higher order point, the number of the PDUs collected at one point increases as the PDUs go up to a higher order point, an unexpected volume of PDUs are concentrated at one time, and a problem occurs such that they become stacked due to a buffer becoming full and the limitations of the processing capability.
Particularly when, in the common management information protocol (CMIP) of a network management system, protocol failures in the apparatus are collected at a higher order point as alarms, they are transmitted using an m-event-report, which causes the above-mentioned problems.
FIGS. 1A and 1B explain a conventional apparatus in which CMIP is adopted.
CMIP is an open system interconnection (OSI) network management protocol for collectively managing resources relating to an open system, and is positioned in an application layer of an OSI basic reference model. CMIP is specified in X.711 and ISO (International Standards Organization) 09596.
As shown in FIG. 1A, the basic model of OSI management specifies communications between a managing side system 1100 and a managed side system 1101. A manager 1102 manages a managed object (MO) 1104 in the managed side system 1101 through an agent 1103. Accordingly, by defining the operation of an MO 1104 in relation to the network, the manager 1102 can manage the network. The manager 1102 operates the MO 1104 by various kinds of CMIP operations, and receives events which occur in the MO 1104 as a report.
FIG. 1A shows a system management model specified in the OSI management.
Resources to be managed are extracted and a system is managed as an MO 1104 provided corresponding to each resource. There are the two concepts of an MO class and an MO instance in the MO 1104. The MO class is a definition of common characteristics for a plurality of concrete management targets (MO instances), whereas the MO instance is a concrete management target for representing an MO class.
In the MO class, attributes possessed by the MO 1104, operations given to the MO 1104, reactions to the operations, reports from the MO 1104, etc. are defined.
The CMIP operations can be roughly divided into management operations of the manager 1102 for the agent 1103, and reports from the agent 1103 to the manager 1102.
Management operations include m-get, m-set, m-action, m-create and m-delete. The commands m-get, m-set, m-action, m-create and m-delete are for obtaining attribute values, setting attribute values, operating the MO 1104, adding the MO 1104 and deleting the MO 1104, respectively.
There is a command called an m-event-report for generating a report from the MO 1104 to the manager 1102.
FIG. 1B shows the configuration of a PDU of an m-event-report.
The parameters of the m-event-report include an invoke identifier, mode, class identifier, instance identifier, event type, event time and event information. The invoke identifier designates an identifier assigned to a report. Each operation is distinguished by this identifier. The mode designates a particular mode of the m-event-report. The managed object class (MO class) of the class identifier designates the MO class in which an event occurs. The managed object instance (MO instance) of the instance identifier designates the MO instance in which an event occurs. The event type designates the type of an event to be reported. The event time indicates the time when an event occurs. The event information includes information on events. By means of a PDU including an m-event-report command containing each of these parameters, an alarm is reported to a higher order point. Here, an event means any change of state which occurs at each point, such as occurrence of a buffer-full state.
The apparatus form of the managed side system is not specified. As described before, the model of the OSI management specifies only communications between the manager 1102 and agent 1103. However, it is often the case that here and there in the apparatus, information of an event is transmitted in a form including a PDU of an m-event-report, and the collecting form of the alarms has a hierarchical structure. The larger the scale of a network, the stronger this tendency becomes.
When a network has a tree-structure with three or more layers, a communication method in which PDUs are transmitted from a lower order point to a higher point, and the PDUs are collected at the higher order point, a problem occurs such that the number of PDUs collected at one point increases as the PDUs go up to a higher order point, and then an unexpected volume of PDUs are concentrated at one time, so they are stacked due to a buffer becoming full and the limitations of the processing capability. At that time, in such a procedure as buffer resetting executed because a buffer has become full, or a CPU resetting, all PDUs are discarded, even if some of the PDUs contain important information. However, despite a buffer being full in a certain place on a network, there is a possibility that an empty buffer exists elsewhere on the network. It is because buffer information is not transmitted and received between higher and lower order points that these buffers cannot be effectively used. Further, when a buffer is full and a user wants to eliminate a PDU, the PDU is indiscriminately eliminated, since it cannot be judged whether or not the PDU contains important information.
It is an object of the present invention to provide a communication apparatus in which a buffer on a network is effectively used by transmitting and receiving buffer information between a higher order point and a lower order point on a network having a tree-structure and in which important information cannot be easily eliminated.
The communication control apparatus of the present invention is used in a system where a plurality of monitoring target units are connected on a tree-shaped network, and each monitoring target unit comprises a receiving unit for receiving data from a lower order monitoring target unit on a tree-shaped network, a buffering unit for temporarily storing the received data, a transmitting unit for transmitting data stored in the buffering unit to a higher order monitoring target unit on the tree-shaped network, and a monitoring unit for monitoring the volume of data stored in the buffering unit, and instructing the lower order monitoring unit not to transmit the data to a higher order monitoring target unit when the data volume exceeds a predetermined threshold.
The communication control method of the present invention is a communication control method used in a system in which a plurality of monitoring target units are connected on a tree-shaped network, and which comprises a receiving step for receiving data from a lower order monitoring target unit on a tree-shaped network, a step for temporarily storing the received data, a transmitting step for transmitting the data stored temporarily to a higher order monitoring target unit on the tree-shaped network, and a step for monitoring the volume of the data stored, and instructing the lower order monitoring unit not to transmit the data to a higher order monitoring target unit when the data volume exceeds a predetermined threshold.
According to the present invention, when data (reporting occurrence of a failure, etc.) transmitted from a lower order monitoring target unit (point) is collected in a higher order monitoring target unit, the collected data volume in the higher order monitoring target unit increases, and a buffer for receiving the data often overflows, since a network is structured in a tree shape. For this reason, the apparatus is configured so as to compare the data volume in the buffer with a predetermined threshold and to instruct a lower order monitoring unit which transmits data not to transmit the data when the data volume in the buffer exceeds the threshold. Thus, the buffer of one monitoring target unit can be prevented from overflowing, and the buffers for the whole network can be effectively used, since data not transmitted is stored in the buffer of a lower monitoring target unit.